1. Field of the Invention
The present invention relates to a wind turbine blade pitch-control system for changing the pitch angles of wind turbine blades, and to a wind turbine rotor and wind turbine generator provided with the same.
2. Description of Related Art
Standard propeller-type wind turbine generators are equipped with a wind turbine rotor in which a plurality of wind turbine blades are attached to a rotor hub serving as a rotation center. These blades are configured so that the wind turbine rotor is rotatably supported at a surface on the upwind side of a nacelle that is supported at the top of a tower in a manner allowing yawing thereof, and a generator installed inside the nacelle is driven by rotation of the wind turbine rotor to perform power generation. In the case of an upwind-type wind turbine generator, the nacelle is subjected to slew driving control so that the rotational center axis of the rotor hub (wind turbine rotor) always points in the upwind direction, which enables efficient power generation.
In recent years, as disclosed in Patent Literature 1 etc., pitch-control systems that rotate the individual wind turbine blades provided on the wind turbine rotor relative to the rotor hub by means of a driving source, such as hydraulic oil, so as to change the pitch angle (angle of attack) of each wind turbine blade have been installed. With this pitch-control system, the wind turbine blades are rotated to the fine side, where the pitch angle is greater, at the time of weak wind force and are rotated to the feather side, where the pitch angle is smaller, at the time of strong wind force. By doing so, it is possible to cause the generator to generate power close to the desirable rotational speed.
In the wind turbine generator disclosed in Japanese Unexamined Patent Application, Publication No. 2008-291789, as shown in FIGS. 3 to 6 therein, a middle portion of a cylinder for changing the pitch angle of a wind turbine blade is supported, in a freely oscillating manner, by a trunnion bearing provided on the rotor hub. The wind turbine generator has a configuration in which the end of a rod that extends in an extendible/retractable manner from this cylinder is coupled in a freely rotatable manner to a coupling shaft provided on a root-side end face of the wind turbine blade (the end face of the wind turbine blade inside the hub) at a decentered position relative to the pitch rotation axis via a spherical bearing (rod bearing), and the wind turbine blade rotates by the extension/retraction of the rod so as to change the pitch angle.
However, because the middle portion of the cylinder is supported at the front end face of the rotor hub via the trunnion bearing, as described above, the structure of the pitch-control system becomes complex, causing the weight around the cylinder to increase, and there is a demand for an improved wind turbine rotor with a simpler structure and lower weight. However, the trunnion bearing, which has a complex structure, is expensive and difficult to maintain, resulting in the problem of running up construction costs and running costs of wind turbine generators.
In addition, because the trunnion bearing must, by necessity, have a large outer diameter from a structural viewpoint, a large hole must be formed in the rotor hub for passing the trunnion bearing therethrough, and this is one factor that ruins the strength of the rotor hub.
To efficiently convert the extending/retracting force of the cylinder to a rotational force of the wind turbine blade, the axes of the cylinder and the rod preferably should be parallel to the root-side end face of the wind turbine blade. However, because the trunnion bearing is large, as described above, in order to prevent interference with the root-side end face of the wind turbine blade, it is necessary to locate the trunnion bearing sufficiently far from the root-side end face of the wind turbine blade. Accordingly, the height of a coupling shaft to which the end of the rod is coupled at the root-side end face of the wind turbine blade, as described above, inevitable must be high. Therefore, the extending/retracting force of the rod ends up exerting a large bending moment at the base of the coupling shaft, and the coupling shaft is easily damaged, causing concern that the durability of the pitch-control system is reduced.